Mastication is conducted by masticatory movements which are made by intricate combinations of the functions of many organs and tissues such as the teeth, periodontal tissues, musculi masticatorii, articulatio temporomandibularises, tongue, labia oris, genae, and salivary secretion organs. Therefore, it is difficult to absolutely and objectively estimate masticatory efficiency.
As one of the conventional methods for testing masticatory efficiency, a method is known which comprises the steps of having a subject put actual food into his mouth, masticate it and spit it out, and then estimating the size of the pieces of masticated food. For example, the subject chews a certain amount of raw rice or peanuts and spits out the chewed food, which is then passed through sieves of certain mesh sizes. The pieces of food on each sieve are dried and weighed. A subject who produces a larger amount of fine chewed food is considered to have higher masticatory efficiency (Comprehensive Dictionary of Dentistry and Medicine, published by ISHIYAKU PUBLISHING CO. LTD., 1988, pp. 1628-1629).
This method for testing masticatory efficiency using raw rice or peanuts described in the above reference is practical in that actual food is used, and the values obtained as a result of the method are persuasive. However, the method has disadvantages in that the procedure is complicated, special tools are necessary, a technician who has mastered the use of the tools is required, it is difficult to standardize the quality of the food, and a large number of tests can not be carried out in a short time.
Other methods have also been developed. In one a piezoelectric element is used to measure biting strength, which is one of the factors of masticatory efficiency, and in another the weak voltage produced in the muscles around the articulatio temporomandibularises is measured. These methods have advantages in that the values obtained are objective and accurate since the biting strength is electrically measured, and that any suitable sensitivity can be selected. However, the methods have disadvantages in that biting strength does not always have a good correlative relation with masticatory efficiency, special tools are necessary for the measurement, and a trained technician is required for the measurement.
Other methods include: the chewing gum method which comprises the steps of having a subject masticate a certain amount of chewing gum containing sugar a certain number of chewing cycles, and measuring the amount of sugar eluted into the saliva; a method which comprises the steps of having a subject masticate granules of adenosine triphosphate disodium (hereinafter referred to as "ATP-G") a certain number of chewing cycles, and determining the amount of ATP-G eluted into the saliva; and the jelly method of estimating a subject's taste for jellies in five grades using several kinds of jellies differing in size and hardness. These methods have advantages in that the procedures for the measurement are simple, the test food can be easily standarized, and the test food is similar to ordinary food. However, the chewing gum method is difficult to use with a subject who wears a full set of dentures. The ATP-G method can not be used for measuring overall masticatory efficiency because the subject unconsciously masticates the granules only at the occlusal portions usually used. The jelly method is an organoleptic test and therefore is not objective. All of the aforementioned methods for testing masticatory efficiency have disadvantages when applied to testing the masticatory efficiency of Japanese subjects since the test food has physical properties different from the foods which Japanese typically prefer but are hard to bite off, such as rubbery vinegared octopus and boiled fish paste. Moreover, the measurements require special instruments such as a photometer that can be operated only by a skilled technician.